From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([59.151.112.132]:25429 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752812AbcAVM0T convert rfc822-to-8bit (ORCPT ); Fri, 22 Jan 2016 07:26:19 -0500 From: Zhao Lei To: "'Chris Mason'" CC: References: <9d3a1b584cec0081382f832ab0a7f9b31b1d9798.1452584763.git.zhaolei@cn.fujitsu.com> <20160120151627.kuy3auwiguoe6xc6@floor.thefacebook.com> <20160120174823.ck5zeoihwsrbvoih@floor.thefacebook.com> <00a501d15433$61275d10$23761730$@cn.fujitsu.com> <20160121141444.gygz5lrkerq67lxz@floor.thefacebook.com> In-Reply-To: <20160121141444.gygz5lrkerq67lxz@floor.thefacebook.com> Subject: RE: [PATCH 1/2] btrfs: reada: limit max works count Date: Fri, 22 Jan 2016 20:25:56 +0800 Message-ID: <00ce01d15510$0b35adc0$21a10940$@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hi, Chris Mason > -----Original Message----- > From: Chris Mason [mailto:clm@fb.com] > Sent: Thursday, January 21, 2016 10:15 PM > To: Zhao Lei > Cc: linux-btrfs@vger.kernel.org > Subject: Re: [PATCH 1/2] btrfs: reada: limit max works count > > On Thu, Jan 21, 2016 at 06:06:21PM +0800, Zhao Lei wrote: > > Hi, Chris Mason > > > > > -----Original Message----- > > > From: Chris Mason [mailto:clm@fb.com] > > > Sent: Thursday, January 21, 2016 1:48 AM > > > To: Zhao Lei ; linux-btrfs@vger.kernel.org > > > Subject: Re: [PATCH 1/2] btrfs: reada: limit max works count > > > > > > On Wed, Jan 20, 2016 at 10:16:27AM -0500, Chris Mason wrote: > > > > On Tue, Jan 12, 2016 at 03:46:26PM +0800, Zhao Lei wrote: > > > > > reada create 2 works for each level of tree in recursion. > > > > > > > > > > In case of a tree having many levels, the number of created > > > > > works is 2^level_of_tree. > > > > > Actually we don't need so many works in parallel, this patch > > > > > limit max works to BTRFS_MAX_MIRRORS * 2. > > > > > > > > Hi, > > > > > > > > I don't think you end up calling atomic_dec() for every time that > > > > reada_start_machine() is called. Also, I'd rather not have a > > > > global static variable to limit the parallel workers, when we have > > > > more than one FS mounted it'll end up limiting things too much. > > > > > > > > With this patch applied, I'm seeing deadlocks during btrfs/066. You > > > > have to run the scrub tests as well, basically we're just getting > > > > fsstress run alongside scrub. > > > > > > > > I'll run a few more times with it reverted to make sure, but I > > > > think it's the root cause. > > > > > > I spoke too soon, it ended up deadlocking a few tests later. > > > > > In logic, even if the calculation of atomic_dec() in this patch having > > bug, in worst condition, reada will works in single-thread mode, and > > will not introduce deadlock. > > > > And by looking the backtrace in this mail, maybe it is caused by > > reada_control->elems in someplace of this patchset. > > > > I recheck xfstests/066 in both vm and physical machine, on top of my > > pull-request git today, with btrfs-progs 4.4 for many times, but had not > triggered the bug. > > Just running 066 alone doesn't trigger it for me. I have to run everything from > 00->066. > > My setup is 5 drives. I use a script to carve them up into logical volumes, 5 for > the test device and 5 for the scratch pool. I think it should reproduce with a > single drive, if you still can't trigger I'll confirm that. > > > > > Could you tell me your test environment(TEST_DEV size, mount option), > > and odds of fails in btrfs/066? > > 100% odds of failing, one time it made it up to btrfs/072. I think more > important than the drive setup is that I have all the debugging on. > CONFIG_DEBUG_PAGEALLOC, spinlock debugging, mutex debugging and lock > dep enabled. > Thanks for your answer. But unfortunately I hadn't reproduce the dead_lock in above way today... Now I queued loop of above reproduce script in more nodes, and hopes it can happen in this weekend. And by reviewing code, I found a problem which can introduce similar bad result in logic, and made a patch for it. [PATCH] [RFC] btrfs: reada: avoid undone reada extents in btrfs_reada_wait Because it is only a problem in logic, but rarely happened, I only confirmed no-problem after patch applied. Sorry for increased your works, could you apply this patch and test is it works? Thanks Zhaolei > -chris